In general, when the presence or absence of scratches, pinholes, distortion or the like formed on the surface of a subject to be inspected is inspected with a photosensor device of such a type, a casing of this device is disposed opposite to the surface of the subject to be inspected at a predetermined distance, inspection light is applied to the subject to be inspected from a light-applying fiber installed in this casing, and reflected light from the subject to be inspected is received by a photosensor through a light-receiving fiber.
The reflected light received by the photosensor is photoelectrically converted and output to an arithmetic section, and it is judged whether or not the voltage value (received light intensity) is within a certain set value. At that time, when scratches, pinholes, distortion or the like exist on the surface of the subject to be inspected, the reflected light is scattered or deflected, whereby the received light intensity detected by the photosensor decreases. As a result, when the received light intensity (voltage value) detected by the photosensor is less than a certain set level, an inspector may judge that scratches or the like exist on the surface of the subject to be inspected.
Incidentally, in many cases, the light-applying fiber installed in the casing is extended from this casing and connected to a light source device prepared at the outside, and inspection light emitted from a light source such as a semiconductor laser installed in the light source device is applied to the subject to be inspected via the light-applying fiber.
When the distance between the photosensor and the light source device is relatively long, it is demanded to sufficiently guarantee the strength and durability, whereby the cost becomes high. Further, the optical fiber connecting them has a flexibility and is thus likely to tremble, and when the optical fiber trembles, noise is likely to be made and properties of the inspection light tend to change, such being inconvenient.
Further, a connector portion which connects the optical fiber and the light source device is likely to be overloaded, and therefore it is also demanded to sufficiently guarantee the durability of this connector portion.
On the other hand, in general, optical disks such as CD (compact disk) are prepared by forming a recording film by coating on the surface of a polycarbonate resin substrate, and further providing a reflecting film on its surface. If defects such as scratches exist on the reflecting film or the like, recording properties will be remarkably impaired. Accordingly, various inspection devices to detect the defects have been proposed.
For example, JP-A-2000-171405 discloses a disk inspection apparatus in which a laser beam is irradiated on a rotating magnetic recording disk, and reflected light is received by a CCD array, and luminance data of each received pixel is compared with a preliminarily set luminance threshold to judge the presence or absence of defects on the disk surface.
However, in the disk inspection apparatus disclosed in the above publication, an expensive CCD array is used as an element to receive the reflected light from the disk, and further a means for image processing by each pixel the results obtained from the light received by the CCD array, whereby the structure is complicated and the unit cost of product is high. Accordingly, provision of the disk inspection apparatus of this type in a plural number in production steps leads to rise of the cost for equipment and is therefore unlikely to be realized.
As a result, since the disk inspection apparatus is used for inspection of finished disks only, even if defects are formed during the production steps, the defects will not be found until completion of production, whereby the yield of products is low, such being problematic.